Blood pumps are used to provide support for the left, the right, or both heart ventricles. These so called left ventricular assist devices (LVAD), right ventricular assist devices (RVAD) or biventricular assist devices (BVAD) can be used to maintain the mechanical functions of the heart while a patient awaits a heart transplantation, or recovers after a heart disease such as a myocardial infarction. In the following the above ventricular assist devices are abbreviated by VAD. VAD systems can be implanted, such that the discomfort for the patient is minimized. In order to determine how much blood needs to be pumped by the pump, methods for measuring the blood flow have been commercialized.
VAD systems often produce a flow which circumnavigates one of the heart's valves such as the aortic, mitral or pulmonary valve. However, it is desired that the heart valves functions are maintained. Thus, a need exists to determine whether one of the heart valves opens or closes during a heart cycle including a single systole and diastole during pump operation.
U.S. Pat. No. 6,066,086 discloses a method for controlling the speed of a blood pump wherein the speed of the blood pump is controlled by determining a valve state of each of the atrial and mitral valves by either the motor current or by using acoustic information of the heart. In order to determine whether said valves are open or closed, the document suggests an acoustic transducer to listen to heart sounds and to output a signal to a micro processor whether the valves where open or not.
US 2010/0222634 A1 discloses a blood pump wherein the state of the aortic valve is assumed to be open when a left ventricular pressure is equal to the aortic pressure or the left ventricular pressure is greater than the arterial pressure. In order to measure both pressures the blood pump includes a first sensor located at an inflow conduit and a second sensor located at an outflow conduit. The document further assumes that the blood pressure at the inflow conduit in an LVAD reflects the left ventricular pressure, while the second sensor located at the outflow conduit reflects the aortic pressure. However, the method is based on the assumption that if the left ventricular pressure was greater or equal than the arterial pressure, then the aortic valve was open. However, the state of the aortic valve cannot be reliably deduced from the ventricular and arterial pressure values only.